As a next generation radio communication method of a world standard, an LTE (Long Term Evolution) system is standardized by 3GPP (3rd Generation Partnership Project). The 3GPP and NGMN (Next Generation Mobile Network) have been consulting as to SON (Self Organizing Network) for the purpose of a reduction in maintenance cost by operators and automated network optimization in the LTE system. Functions of the SON are classified into four categories: Planning, Development, Optimization and Maintenance. It has been expected to substantialize a stable network by adopting the functions of the SON to efficient maintenance/configuration/planning of the network such as optimization of radio parameters and network parameters, interference control and addition of a neighbor cell list. Especially if a self-configuration process and a self-optimization process are substantialized by automation of works that used to be manually operated by the operators, network maintenance cost may be minimized. The self-configuration process is defined as a process, in installation of a new base station apparatus eNB (evolved Node B), for automatically acquiring and setting a basic parameter necessary for system maintenance. The self-configuration process is considered as a process conducted mainly before the base station apparatus comes into an operation state. The self-optimization process is defined as a process, based on statistical data from a terminal UE (User Equipment) and a base station apparatus, for performing automatic regulation of the network. The self-optimization process is considered as a process started after start-up of an RF apparatus and conducted when the base station apparatus is in the operation state. An example of the self-optimization process is optimization of a neighboring base station list.
One of more detailed aims of SON is to automatically set PCI (Physical Cell ID), which is an identification number of a cell of the base station apparatus. The PCI is a parameter inevitable for the cell and the terminal needs the PCI in order to synchronize with the cell. Since the number of unique PCIs that E-UTRAN (Evolved Universal Terrestrial Radio Access Network), one specification of LTE, may have is limited to 504, it is unavoidable to assign the same PCI to different cells when the number of cells exceeds 504. However, when the cells with the same PCI are positioned close to one another, communications of the cells are interfered, possibly disabling a voice call or handover. Therefore, it is necessary to satisfy two conditions: (1) the PCI of a first cell of a first base station must be different from the PCI of a second cell of a second base station adjacent to the first base station, and (2) the PCI of the first cell of the first base station must be different from the PCI of a third cell of a third base station adjacent to the second base station. The base station apparatus may acquire information about the PCI of the cell of the neighboring base station apparatus from the neighboring base station list (neighbor cell list) held by each base station apparatus.
Recently, 3GPP has been suggesting a framework in which, when a new base station apparatus is installed, the new base station apparatus autonomously selects and sets the PCI for the cell thereof (for example, see Non-Patent Document 1 listed below). In detail, the base station apparatus selects the PCI of the cell thereof based on Centralized PCI assignment algorithm or distributed PCI assignment algorithm. According to Centralized PCI assignment algorithm, the base station apparatus is notified of a unique PCI by OAM (Operation Administration and Maintenance) and sets the unique PCI for the cell thereof. On the other hand, according to distributed PCI assignment algorithm, the base station apparatus is notified of a PCI list including available PCIs by OAM and, by removing unsuitable PCIs from the list, selects any PCI remained in the list and sets the PCI for the cell thereof.
In addition to Centralized PCI assignment algorithm and distributed PCI assignment algorithm described above for setting the PCI before start-up of the new base station apparatus, there is also suggested a method for setting the PCI after start-up of the new base station apparatus (for example, see Non-Patent Document 2). According to this method, the new base station apparatus first selects any value from 504 candidate PCIs as Temporary PCI in a configuration phase and is started up. Then, the new base station apparatus, with an ANR (Automatic Neighbor Relation) function, acquires information about the neighboring base station apparatuses notified by the terminals and creates the neighboring base station list. Further, the new base station apparatus obtains the neighboring base station list from the neighboring base station apparatuses. The new base station apparatus then selects the PCI satisfying both of the above conditions (1) and (2) from the created neighboring base station list and the acquired neighboring base station list.